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| Natura: | Preprint |
| Pubblicazione: |
2025
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| Accesso online: | https://arxiv.org/abs/2508.11819 |
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| _version_ | 1866913993678913536 |
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| author | Wang, Q. Daniel Ott, Juergen |
| author_facet | Wang, Q. Daniel Ott, Juergen |
| contents | Using a 90 ks Chandra ACIS-S observation in the 0.3--7 keV band, along with complementary Low-Frequency Array and Karl G.~Jansky Very Large Array data in the 120--168 MHz and 1--2 GHz ranges, we study the diffuse emission around the nearby dwarf galaxy KUG~1138+327. Our analysis reveals a diffuse X-ray feature on the southern side, disconnected from the galactic disk. This feature exhibits a hard X-ray spectrum, which is highly unusual for an outflow from a dwarf galaxy. We interpret the irregularly shaped feature as hot plasma in a young galaxy cluster at redshift 0.5, supported by X-ray spectral fitting and consistent with the optical redshift of the central elliptical galaxy of a known cluster identified by a red sequence. Additionally, we detect a radio lobe east of the X-ray feature, likely produced by an AGN offset from the cluster center and confined primarily by ram pressure from the ambient medium. The lobe shows a steep nonthermal radio spectrum, suggesting a cosmic-ray age of $\gtrsim 5 \times 10^{7}$~yr. Assuming energy equipartition between cosmic rays and magnetic fields, we estimate the lobe's total energy to be $\sim 9 \times 10^{56}~\mathrm{erg}$, comparable to the thermal energy in the same volume. This study thus identifies a background young cluster projected next to KUG~1138+327 and highlights the potentially significant role of off-center AGN feedback in shaping the intracluster medium. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_11819 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Serendipitous discovery of a young cluster of galaxies at $z \sim 0.5$ projected next to the nearby tadpole galaxy KUG 1138 + 327 Wang, Q. Daniel Ott, Juergen High Energy Astrophysical Phenomena Using a 90 ks Chandra ACIS-S observation in the 0.3--7 keV band, along with complementary Low-Frequency Array and Karl G.~Jansky Very Large Array data in the 120--168 MHz and 1--2 GHz ranges, we study the diffuse emission around the nearby dwarf galaxy KUG~1138+327. Our analysis reveals a diffuse X-ray feature on the southern side, disconnected from the galactic disk. This feature exhibits a hard X-ray spectrum, which is highly unusual for an outflow from a dwarf galaxy. We interpret the irregularly shaped feature as hot plasma in a young galaxy cluster at redshift 0.5, supported by X-ray spectral fitting and consistent with the optical redshift of the central elliptical galaxy of a known cluster identified by a red sequence. Additionally, we detect a radio lobe east of the X-ray feature, likely produced by an AGN offset from the cluster center and confined primarily by ram pressure from the ambient medium. The lobe shows a steep nonthermal radio spectrum, suggesting a cosmic-ray age of $\gtrsim 5 \times 10^{7}$~yr. Assuming energy equipartition between cosmic rays and magnetic fields, we estimate the lobe's total energy to be $\sim 9 \times 10^{56}~\mathrm{erg}$, comparable to the thermal energy in the same volume. This study thus identifies a background young cluster projected next to KUG~1138+327 and highlights the potentially significant role of off-center AGN feedback in shaping the intracluster medium. |
| title | Serendipitous discovery of a young cluster of galaxies at $z \sim 0.5$ projected next to the nearby tadpole galaxy KUG 1138 + 327 |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2508.11819 |